Monitoring of wearing surface layer thickness

ABSTRACT

A method of wear level determination and an associated product. Multiple Radio Frequency IDentification (RFID) tags are distributed within a thickness of a wearing surface layer of a tire. The multiple RFID tags include first RFID tags that have not been worn away, second RFID tags that have been worn away, and a special RFID tag that has not been worn away. A measure of wear of the wearing surface layer of the tire is determined from data received from the first RFID tags and from a table in the special RFID tag. The product includes the wearing surface layer of the tire, the multiple RFID tags, and a mechanism for determining the measure of wear of the wearing surface layer.

This application is a continuation application claiming priority to Ser.No. 11/255,390, filed Oct. 20, 2005.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method, system, and product formonitoring of wearing surface layer thickness.

2. Related Art

Because tires are the only points of contact between a vehicle and theroad, tires are one of the most crucial safety components in thevehicle, for all types of vehicles, such as cars, trucks, sport utilityvehicles, off-road vehicles, airplanes, motorcycles, bicycles, mobileindustrial and construction equipment, and the like. Tires areresponsible for how the vehicle responds to the driving and steering. Tooptimize the effects of the tires on the road and therefore, to providea safety behavior of the vehicle, the inflation pressure of the tiresmust be kept within the range given by the manufacturer. Tires that aredriven under-inflated generate excessively high heat levels that canweaken the tire to the point of failure. At high speed, a rapidlydeflating tire can cause loss of vehicle control. An over-inflated tirewill result in harsh ride quality and will cause uneven tire wear.Furthermore, operating a vehicle with over- or under-inflated tiresincreases both fuel consumption and the exhaust emissions produced bythe vehicle.

Tires are designed to grip the road, allowing the vehicle to start, stopand go around corners safely in any weather. Proper treads allow fornormal handling of a vehicle and help prevent skidding and hydroplaning.The treads that accomplishes this wear out over time. As a consequence,the distance that is required to stop a vehicle increase with the wearof tires. A recent series of tests conducted for The British RubberManufacturers Association by MIRA has shown that the stopping distancesignificantly increases and cornering performance deteriorates when tiretread depth falls below 3 mm, even if the legal minimum tread depth is1.6 mm (generally, the tire tread depth is comprised between 7 and 9mm). So, it is extremely important to check the tire treads for signs ofwear.

Generally, tires are manufactured with a “wear bar” that tells when theremaining tread depth is less than the minimum legally required e.g.,1.6 mm. When this wear bar can be seen, the tire must be replaced. Otherknown marking devices disappear when the wear of the treads becomescritical. However, a main drawback of these systems is that wear oftires must be done wheel after wheel, when the vehicle is stopped,according to a manual or visual analysis that is often painful due tothe location of the wheels in the vehicle wings.

In other known methods, acoustic wear indicators emit a sound signal bycoming into contact with the ground when the tires reach a wearthreshold level. An automatic monitoring is done by using a detectorconsisting of a microphone placed beneath the vehicle and a processingunit switches on an indicator placed in the instrument panel. If suchsolution allows an automatic control of the tire wear, it closelydepends upon the vehicle environment and driving conditions andtherefore, it could be complex to implement.

SUMMARY OF THE INVENTION

The present invention provides a product comprising a wearing surfacelayer and at least one Radio Frequency IDentification (RFID) tag withina thickness of the wearing surface layer, the wearing surface layerbeing an outermost surface layer of the product, the wearing surfacelayer adapted to be worn away such that a thickness of the wearingsurface layer is reduced as the product is being used.

The present invention provides a method of wear level determination,comprising:

receiving data from at least one Radio Frequency IDentification (RFID)tag within a thickness of a wearing surface layer of each product of atleast one product, the wearing surface layer of each product being anoutermost surface layer of said each product, the wearing surface layerof said each product adapted to be worn away such that the thickness ofthe wearing surface layer is reduced as said each product is being used;and

determining a measure of wear of the wearing surface layer of eachproduct of the least one product from said received data.

The present invention remedies the shortcomings of the prior artdescribed supra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 1B illustrate a Radio Frequency IDentification (RFID) systemcomprising a RFID tag and a reader, in accordance with embodiments ofthe present invention.

FIG. 2 depicts a cross section view of a tire embedding two RFIDs usedto monitor the tire wear, in accordance with embodiments of the presentinvention.

FIG. 3, comprising FIG. 3 a and FIG. 3 b, shows schematically twoexamples of reader implementation within a car, in accordance withembodiments of the present invention.

FIG. 4, comprising FIGS. 4 a and 4 b, illustrates examples of algorithmsthat could be used in conjunction with readers for determining tirewear, in accordance with embodiments of the present invention.

FIG. 5, comprising FIGS. 5 a, 5 b, and 5 c, showing partial crosssection views of a tire, depicts examples of the implementation of RFIDsin a tire, as well as the data stored in these RFIDs, in accordance withembodiments of the present invention.

FIG. 6, showing a partial cross section view of a tire, illustrates anexample of the implementation of RFIDs in a tire that allows themonitoring of tire wear and of tire wear balance, in accordance withembodiments of the present invention.

FIG. 7 shows an example of an algorithm for monitoring tire wearbalance, in accordance with embodiments of the present invention.

FIG. 8 illustrates a partial cross section view of a tire embeddingRFIDs that one stores the spacial locations of these RFIDs, inaccordance with embodiments of the present invention.

FIG. 9 is a table in which identifiers and spatial locations of RFIDsare stored, in accordance with embodiments of the present invention.

FIG. 10 shows an example of an algorithm used to monitor wear of tireembedding RFIDs that at least one comprises spatial locations of theseRFIDs, in accordance with embodiments of the present invention.

FIG. 11 illustrates an example of an algorithm allowing thedetermination of the number of sets of RFIDs in a tire for monitoringtire wear balance, in accordance with embodiments of the presentinvention.

FIG. 12 depicts the table of FIG. 9 further comprising informationrelative to the date and mileage at which RFIDs have been extracted fromthe tire, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides method and system for monitoring tirewear and tire wear balance. According to the present invention, RadioFrequency IDentifications (RFIDs) are embedded within the tire tread ofthe tire to monitor, at different distances from the periphery of thetire (i.e., at different depths within the thickness of the tread). Aslong as the tire wear increases, the thickness of the rubber decreasesand RFIDs are removed. By monitoring the remaining RFIDs and analyzingtheir signatures, one can determine tire wear. Likewise, a plurality ofRFIDs can be distributed along the tire width, at approximatelyequivalent distance from the tire periphery, to monitor tire wearbalance.

The present invention provides a method and system for wireless wearmonitoring of tire tread and other surfaces, the tires or surfaces beingin movement or not.

The present invention provides a method and system for wireless wearmonitoring of tire tread and other surfaces that is independent of thetire or surface environment.

The present invention provides a method and system for wireless wearmonitoring of tire tread and other surfaces that do not required anylearning phase.

The present invention provides a product having a wearing surface layer(e.g., tire tread of a tire, the tire adapted to be used in a vehicle)comprising at least one RFID tag characterizing a wear level of saidwearing surface layer, said at least one RFID tag being embedded withinthe thickness of the wearing surface layer.

The wearing surface layer of the object is an outermost surface layer ofthe object. The thickness of the wearing surface layer (i.e., thethickness of the outermost surface layer) extends through the entiredepth of the wearing surface layer and is oriented in a direction thatis perpendicular to an exposed outermost surface of the surface layer ofthe object. The wearing surface layer has a characteristic of being wornaway such that its thickness is reduced as the product is being used. Asan example wherein the product is a tire, the wearing surface layer ofthe tire is the tire tread of the tire, and the thickness of the wearingsurface layer of the tire is the thickness (i.e., the entire depth) ofthe tire tread of the tire. Thus, the thickness of the wearing surfacelayer is dynamically changing by being reduced as the product is beingused.

In the description herein, such terms as “tire wear” and “wear level” ofa tire are each a measure of a portion, fraction, percentage, etc. ofthe original tire tread that has been worn away since the tire tread wasbrand new. More generally, a measure of wear of a wearing surface layeris a measure of a portion, fraction, percentage, etc. of the originalthickness of the wearing surface layer that has been worn away since thewearing surface layer was brand new.

The present invention provides a method for determining the wear levelof a product comprising at least one wearing surface layer, wherein thesaid method comprises for each of said wearing surface layer: readingthe data of the RFID tags embedded within said wearing surface layer;and determining the surface wear from said read data.

The present invention provides a method and system for monitoring wearof tire tread or other surfaces using embedded radio frequencytransponders or Radio Frequency IDentification (RFID) tags, genericallyreferred to as RFIDs in the description herein.

The core of any RFID system is the ‘Tag’ or ‘Transponder’, which can beattached to or embedded within objects, wherein data can be stored. AnRFID reader, generically referred to as reader in the followingdescription, sends out a radio frequency signal to the tag thatbroadcasts back its stored data to the reader. The system worksbasically as two separate antennas, one on the RFID and the other on thereader. The read data can either be transmitted directly to anothersystem like a host computer through standard interfaces, or it can bestored in a portable reader and later uploaded to the computer for dataprocessing. An RFID tag system works effectively in environments withexcessive dirt, dust, moisture, and/or poor visibility. It generallyovercomes the limitations of other automatic identification approaches.

Several kinds of RFID are currently available. For example, passiveRFIDs do not require a battery for RF transmission since generally, thepassive RFIDs are powered by the reader using an induction mechanism (anelectromagnetic field is emitted by the reader antenna and received byan antenna located on the RFID). This power is used by the RFID totransmit a signal back to the reader, carrying the data stored in theRFID. Active RFIDs comprise a battery to transmit a signal to a reader.A signal is emitted at a predefined interval or transmit only whenaddressed by a reader.

When a passive RFID is to be read, the reader sends out a power pulse(e.g., a 134.2 KHz power pulse) to the RFID antenna. The magnetic fieldgenerated is ‘collected’ by the antenna in the RFID that is tuned to thesame frequency. This received energy is rectified and stored on a smallcapacitor within the RFID. When the power pulse has finished, the RFIDimmediately transmits back its data, using the energy stored within itscapacitor as its power source. Generally, 128 bits, including errordetection information, are transmitted over a period of 20 ms. This datais picked up by the receiving antenna and decoded by the reader. Onceall the data has been transmitted, the storage capacitor is discharged,resetting the RFID to make it ready for the next read cycle. The periodbetween transmission pulses is known as the ‘sync time’ and lastsbetween 20 ms and 50 ms depending on the system setup. The transmissiontechnique used between the RFID and the reader is Frequency Shift Keying(FSK) with transmissions generally comprised between 124.2 kHz and 134.2kHz. This approach has comparatively good resistance to noise while alsobeing very cost effective to implement. Many applications require RFIDattached to objects be read while the vehicle is traveling (i.e.,moving) at specific speeds by a readout antenna. With large antennasdesigned for Automatic Vehicle Identification (AVI), it is possible toread successfully data at read speeds of 65 m/s (i.e., 234 km/H).

RFIDs can be read-only, write-once, or read-write. A read-only RFIDcomprises a read-only memory that is loaded during manufacturingprocess. Its content can not be modified. The write-once RFIDs differfrom the read-only RFIDs in that they can be programmed by the end-user,with the required data (e.g., part number or serial number). Theread-write RFIDs allow for full read-write capability, allowing a userto update information stored in a tag as often as possible in the limitof the memory technology. Generally, the number of write cycles islimited to about 500,000 while the number of read cycles is not limited.A detail technical analysis of RFID is disclosed, e.g., in RFID(McGraw-Hill Networking Professional) by Steven Shepard, editionHardcover.

FIGS. 1 a and 1 b collectively illustrate a simple RFID system 100comprising an object 105 on which a RFID 110 is glued. FIG. 1 b is anexpanded view of the RFID 110 of FIG. 1 a. The RFID 110 comprises asupport embedding an antenna 115 and an electronic circuit and memory120. The data contained in the RFID 110 is read by a reader 125connected to a computer 130. In other RFID systems, the RFID readercomprises all the required electronic components to work as a standalone device

In a first embodiment of the present invention, the tire tread orsurface to monitor comprises at least one RFID corresponding to at leastone wear threshold. The wear level is given by the presence or absenceof this at least one RFID. If several RFIDs are embedded within the tiretread or surface to monitor, the data contained in each of them must bedifferent so that the presence of each RFID can be detected.

FIG. 2 depicts a cross section view of an example of a tire 200 havinggrooves 205 designed in the tire tread. The tire 200 comprises a firstRFID 210 located at a distance d1 from the bottom of the grooves and asecond RFID 215 located at a distance d2 from the bottom of the grooves.In this example, the RFIDs are inserted within the rubber mix but itmust be understood that RFIDs can also be positioned and glued withinthe grooves. For sake of illustration, d1 is equal to the minimum legaltreads (i.e., 1.6 mm), and d2 is equal to 3 mm which corresponds to amain change of the tire behavior, as discussed above. When the tire isbrand new and when a soft wear that does not affect the tire behaviorappears, a reader can determine the presence of both RFIDs in the tire,using a known anti-collision algorithm. When a single RFID is detectedin the tire, it means that the tire can still be used but its behaviorhas changed and so, uncertain behavior of the vehicle may occur. When noRFID is detected within a tire, the tire must be changed, since thelegal wear threshold has been reached.

Inserting RFIDs within the tire rubber can be done during manufacturingof the tire. However, in an embodiment, the RFIDs are inserted later(i.e., after manufacturing of the tire), to avoid any manufacturingconstraints such as high pressure and temperature, and to optimize RFIDpositioning accuracy. Therefore, inserting an RFID in less than fewsquare millimeters or even less than one square millimeter within thetire rubber may use a needle that is inserted in the tire at the rightdepth within the thickness of the tire tread such that the RFID is leftin place when the needle is removed.

To detect the presence and absence of RFIDs within tires, one or severalreaders can be used. The reader(s) can be installed within the vehicle,or in a mobile system that is moved near each tire to be tested, or in afixed installation (e.g., in a garage). If a single reader is used tomonitor several tires, the RFIDs embedded within these several tiresmust store different data so that each RFID can be uniquely identified.

The use of RFID technology presents several advantages. Firstly, thetire wear can be monitored: when the vehicle is moving or when it isstopped; when the tires are mounted on wheels or not; and when thewheels are mounted on the vehicle or not. Likewise, the tire wear can bemonitored in most of environmental conditions such as weather conditionsand electromagnetic conditions. Secondly, the monitoring system can beeasily implemented on most of the vehicle and does not require anylearning phase.

FIGS. 3 a and 3 b illustrate schematically the installation of reader(s)within a vehicle. FIG. 3 a shows an example wherein a reader is assignedto each tire to monitor while FIG. 3 b depicts another example wherein asingle reader is used to monitor all the tires.

The vehicle 300 schematically shown on FIG. 3 a comprises four tiresreferred to as 305-fl, 305-fr, 305-rl, and 305-rr (fl, fr, rl, and rrstand for front left, front right, rear left, and rear right,respectively). A reader is associated to each tire to monitor; i.e.,reader 310-fl is associated to tire 305-fl, reader 310-fr is associatedto tire 305-fr, reader 310-rl is associated to tire 305-rl, and reader310-rr is associated to tire 305-rr. All the readers 310-fl, 310-fr,310-rl, and 310-rr, being preferably directional readers, are connectedto a central unit 315. Central unit 315 comprises the interface betweenthe readers and the user; said interface may be a computer or a memory.In its simplest form, central unit 315 comprises a set of LEDsindicating the wear level of each tire. Central unit 315 may comprise anindependent display or can be merged with the vehicle inboard computer.Thus in FIG. 3 a, the vehicle 300 represents a structure that comprisesthe aforementioned four tires, associated RFIDs (305-fl, 305-fr, 305-rl,305-rr) and readers (310-fl, 310-fr, 310-rl, 310-rr), and the centralunit 315.

Since each reader is close to the tire that it monitors, the power ofthe reading signal can be set so as to activating only the RFIDs locatedin a close range (e.g., less than 0.5 m) avoiding ambiguity that couldresults from reading RFIDs of the other tires or any other RFIDs.Therefore, such solution avoids the need of identifying the tires tomonitor.

FIG. 3 b shows a second example of a vehicle 300′, wherein a singlereader 320 coupled to a central unit 325, namely an omni-directionalreader, is used to monitor the wear of all of the four car tires. Asshown, the RFIDs 305′-fl, 305′-fr, 305′-rl, and 305′-rr in FIG. 3 b arerespectively analogous to the RFIDs 305-fl, 305-fr, 305-rl, and 305-rrof FIG. 3 a. To avoid any ambiguity the RFIDs of each tire must beidentified. This can be done by assigning a unique identification numberto each tire, the identification number being stored in each RFID memoryso that comparing the values stored in two RFIDs allows a determinationof whether or not these RFIDs belong to a same tire. Thus in FIG. 3 b,the vehicle 300′ represents a structure that comprises theaforementioned four tires, associated RFIDs (305′-fl, 305′-fr, 305′-rl,305′-rr), the reader 320, and the central unit 325.

An algorithm used to determine the wear level of the tires is shown inFIGS. 4 a and 4 b. FIG. 4 a illustrates the algorithm associated to thereaders when each tire is monitored by an independent reader, while FIG.4 b shows a similar algorithm when a single reader is used to monitorseveral tires.

After having emitted a reading signal, the reader checks the presence ofRFIDs (steps 400 and 405). If no RFID is detected, a warning signal istransmitted to the user to indicate an absence of the tire or toindicate that the tire must be replaced as soon as possible since thewear limit has been reached (step 410). The warning signal can takeseveral forms (e.g., sound, color LED). If at least one RFID isdetected, the reader, or its associated computing unit, determines thenumber n of RFIDs detected using a standard anti-collision algorithm(step 415). Then, the tire wear TW is determined by comparing the numbern of RFIDs still embedded within the tire with the number N of RFIDsthat were embedded in the tire when the tire was brand new (step 420).For example, a measure of wear of the tire tread is the tire wear TWwhich can be estimated in accordance with Equation (1).TW=(N−n)/N  (1)The number N may be stored, for example, in the reader memory 425. Thetire wear may be displayed on a standard display or by means of LEDs,may be stored for further use, or may be used for processing (step 430).

If a single reader is used to monitor several tires, each tire can bechecked sequentially as illustrated in the algorithm depicted on FIG. 4b. An index i, representing a tire i, is set to zero (step 450) and thenumber n(i) of RFIDs still embedded within tire having index i isdetermined (step 455). As mentioned supra, several solutions exist to dosuch determination, the simplest one being to assign a unique identifierto each tire, this unique identifier being copied in each RFID embeddedwithin the corresponding tire. For example, a tire having identifier‘12345’ can comprise 3 RFIDs storing data ‘12345 0’, ‘12345 1’, and‘12345 2’, respectively. Then, the tire wear TW(i), corresponding totire having index i, is computed (step 460) by comparing the number n(i)of RFIDs still embedded in tire having index i with the number N(i) ofRFIDs that were embedded in the tire having index i when it was brandnew. For sake of illustration, a measure of wear of the tire tread ofthe tire I is the tire wear the tire wear TW(i) which can be estimatedin accordance with Equation (2):TW(i)=(N(i)−n(i))/N(i)  (2)

The value N(i) can be stored in the reader memory 465. If the tire wearis equal to one (step 470), then the tire having index i does notcomprise any more RFIDs and so must be changed as soon as possible. Insuch case, a warning may be transmitted to the user by any means of(e.g., light or sound). If the tire wear TW(i) differs from one, thenTW(i) is displayed on a standard display or by means of LEDs, is storedfor further use, or is used for processing (step 480). Then, the index iis incremented by one (step 485) and a test is performed (step 490) todetermine whether or not the value of the index i is equal to a value Irepresenting the number of tires to monitor. Value I can also be storedin the reader memory 465. If the value of index i equals I and thereforedoes not correspond to a tire, then i is reset to zero (step 450) andthe first tire is checked again (steps 455 to 490). Else in step 490, ifthe value of index i is less than I (corresponding to a tire), then thetire having the index i is checked (steps 455 to 490).

Alternatively, the data contains in the RFIDs provides an indication ofthe tire wear. For example, such data can be a wear percentage value, avalue representing the distance between the RFID and the bottom of thegrooves, a value representing the distance between the RFID and the ofthe tire periphery (i.e., exterior surface of the tire tread) when thetire was brand new, etc. For example, considering the tire illustratedon FIG. 2, the RFID 210 can contain the data ‘100%’ (or ‘1.6 mm’) whileRFID 215 contains the data ‘66%’ (or ‘3 mm’). These values may beencoded using standard encoding methods. For example, if tire treadthickness Td is between 1.6 mm and 9 mm and if tire wear data Wd storedin the RFID is coded in one byte (i.e., Wd is between 0 and 255), thenthe values are converted to a measure of wear Wd in accordance withEquation (3):Wd=255×(Td−1.6)/(9−1.6)  (3)

In such case, the tire wear is determined by selecting the smaller wearpercentage value, or the greater tire grooves depth value, among all thevalues extracted from data read in the detected RFIDs. As describedabove, the data can also comprise a tire identifier that can be usedwhen a single reader monitors several tires. Therefore, considering theprevious example, one can conclude that tire wear is less than 66% orthat tire tread thickness is at least equal to 3 mm when reading thedata from RFIDs 210 and 215.

In a second embodiment of the present invention, each tire comprises aset of RFIDs, embedded in the tire at different distances from theperiphery of the tire (i.e., at different depths within the thickness ofthe tread or, equivalently, at different distances from the exteriorsurface of the tire tread), which may be according to a linear (i.e.,spatially uniform) distribution, and storing data comprising ordered andcontinuous values of 1, 2, . . . , 6 corresponding to the rank of theRFID when the tire is brand new. The minimal value (e.g., one), is setclose to the periphery while the greater value is positioned at thegreater distance from the periphery. FIG. 5 a and FIG. 5 b show twoexamples of a partial cross section view of a tire embedding RFIDsaccording to the second embodiment. According to the example illustratedin FIG. 5 a, one reader is used per tire since the data, or rank, storedin the set 500 of RFIDs of two different tires can be the same. Usingtires as the one partially shown on FIG. 5 b, a single reader can beused to monitor several tires since the data stored in each RFID of theset 505 contains a first value representing the tire identifier and asecond value representing the RFID. In the example of FIG. 5 b, thefirst value is the tire identifier ‘12345’ while the second value isvaries from 1 to 6. The extraction of the tire identifier and the RFIDidentifier from the data can be performed using a fixed size format;e.g., 5 bytes for the tire identifier and 1 byte for the RFIDidentifier, or using predetermined delimiter (i.e., a specialcharacter).

For the example of FIG. 5 a and considering that at time t, only RFIDsstoring values 5 and 6 are detected, it is determined that the tire wearis between 50% and 66%. Detecting values 5 and 6 means that when thetire was brand new, the tire was embedding 6 RFIDs. Using Equation (1),since 2 RFIDs are still embedded within the tire, the tire wear TW(t) isless than (6−2)/6 (i.e., 66%), and at a time x before the last RFID waslost the tire was embedding 3 RFIDs corresponding to a tire wear TW(t−x)that was less than (6−3)/6 (i.e., 50%). Therefore, the actual tire wearis between 50% and 66%.

The algorithms presented on FIGS. 4 a and 4 b, described supra, are alsovalid for this second embodiment. However, the values N and N(i) are notstored in the reader memory but are directly determined from the valuesstored in the detected RFIDs. Considering that values stored in theRFIDs are expressed as V(j), where j is an index corresponding to therank of the RFIDs within a tire. Then,N=max_(j)(V(j))  (4)

Likewise, considering that values stored in the RFIDs are expressed asV(i,j), where i is the index corresponding to the tire i, and j is theindex corresponding to the rank of the RFIDs within the tire then,N(i)=max_(j)(V(i,j))  (5)

In a third embodiment of the present invention, a particular RFID (e.g.,the RFID that is located at the greatest distance from the periphery ofthe tire; i.e., the maximum distance from the exterior surface of thetire tread) is used to store additional information. Firstly, thisadditional information is the number of RFIDs that were embedded withinthe tire when it was brand new. In such case, it is not necessary tostore the number of RFIDs in the reader memory as mentioned in the firstembodiment, nor to store particular values in the RFIDs as disclosed inthe second embodiment. In the third embodiment, the algorithms presentedon FIGS. 4 a and 4 b are still valid. However, the values N and N(i) aredirectly read from this particular RFID that can be easily identified byusing a dedicated identifier as illustrated on FIG. 5 c. In the exampleof FIG. 5 c, the identifier to determine the particular RFID 507 of theset 506 is the value zero (i.e., 0) at followed by the number of RFIDs(i.e., 6) that were embedded in the tire when the tire was brand new.The last part of the data in the particular RFID 507 can be used tostore other information such as tire identifier, as depicted.

In a fourth embodiment of the present invention, several RFIDs aredistributed along the tire width, at approximately the same distancefrom the tire periphery, so as to control wear balance along the tirewidth. The tire width is oriented perpendicular to the tire thicknessand perpendicular to the opposite sides of the tire. FIG. 6 shows anexample of such a distribution of RFIDs along the tire width. Asillustrated, a first set 508A of RFIDs (0-0 to 0-5) is embedded withinthe rubber in the tire left part and a second set 508B of RFIDs (1-0 to1-5) is embedded within the rubber of the tire right part. By countingand comparing the number of RFIDs embedded within each set of the tire,one can determine if the tire wear is normal or abnormal (i.e., one cananalyze tire wear balance along the tire width). For example, if thenumber of RFIDs belonging to each set is the same for all the sets or ifthere is only a difference of one RFID, one can conclude that the tirewear is a normal wear (i.e., the tire wear is balanced along the tirewidth), whereas a difference of two or more RFIDs means that the tirewear is an abnormal wear (i.e., the tire wear is unbalanced along thetire width). The greater the difference between the number of RFIDsembedded within each set, the greater the tire wear unbalance is.

In the example given on FIG. 6, the tire comprises only two sets ofRFIDs but it must be understood that the tire can comprises more setsthan two. For example, another set of RFIDs can be implemented in themiddle of the tire. Using several sets of RFIDs disposed along the tirewidth a tire wear profile along the tire width to be determined.

FIG. 7 illustrates an example of an algorithm that can be used inconjunction with a reader that monitors a single wear to detect tirewear and tire wear balance along the tire width. Firstly, an index i,identifying a set of RFIDs in the tire to monitor, is set to zero (step700) and the number of RFIDs embedded within set i in the tire isdetermined (step 705). Determining the number of RFIDs belonging to oneset in a tire comprises analyzing the data stored in the read RFIDs. Forexample, consider data that comprises two parts delimited by a specialcharacter, or having a predetermined coding, the first part being usedto identify the tire set while the second part is an RFID identifier. Inthe example shown on FIG. 6, the special character is ‘-’. Using thenumber N(i) of RFIDs that were embedded within RFID set i in the tirewhen the tire was brand new, the tire wear TW(i) of the tirecorresponding to RFID set i can be determined (step 710). As mentionedsupra, number N(i) can be stored in the reader memory 715 or in aparticular RFID. If the tire wear TW(i) is equal to 1 (step 720), whichmeans that RFID tire set i has tire wear at 100%, a warning istransmitted to the user (step 725). Then, index i is incremented by one(step 730) and a second test is performed (step 740) to determinewhether or not index i is equal to the number imax of sets of RFIDs inthe tire. If i is equal to imax, then the tire wear has been evaluatedfor each monitored RFID set in the tire. The number imax can be storedin the reader memory 715. If I is unequal to imax, then the tire wearhas not been evaluated for each RFID tire set, and steps 705 to 740 arerepeated to evaluate tire wear in the remaining RFID tire sets i, i+1, .. . , imax−1.

Let {TW} denote TW(0), . . . , TW(imax−1). Thus {TW} represents a set oftire wear for the imax RFID sets in the tire. If the tire wear TW(i) hasbeen evaluated for each RFID tire set i (i=0, 1, . . . , imax−1)), afurther test is performed in step 745 to determine if the maximum tirewear difference F({TW}) among the imax RFID tire sets is greater than apredetermined threshold T; i.e., if F({TW})>T. The tire wear differenceF({TW}) is a measure of the tire wear balance along the tire width. IfF({TW})>T, then a warning is transmitted to the user (step 750). Thethreshold T can be stored, for example, in the reader memory 715, asdiscussed supra. The function F({TW}) may be represented, for example,according to Equation (6):F({TW})=max_(j,k)(abs(TW(j)−TW(k))  (6)corresponding to the maximum difference in tire wear between two RFIDsets of the imax RFID sets in the tire, wherein said two RFID sets areidentified by the indexes j and k in Equation (6).

The mean tire wear of {TW} is computed according to the function M({TW})that is either displayed, used for processing, or stored for futureprocessing (step 755), and the monitoring cycle is repeated beginning atstep 700, as shown. The function M({TW}) may be represented, forexample, according to Equation (7):M({TW})=Σ_(i)(TW(i))/imax  (7)

In a fifth embodiment of the present invention, a particular RFID thatis analogous to the particular RFID 507 in FIG. 5 c in relation to thethird embodiment, can be used to store a spatial description of theRFIDs within each tire, to determine their relative position accordingto the rotation axle and the radius of the tire. FIG. 8 depicts apartial cross section view of a tire embedding RFIDs 800-i and a specialRFID 805. The special RFID 805 of the fifth embodiment is analogous tothe particular RFID of the third embodiment (e.g., the particular RFID507 in FIG. 5 c). Reference axis determining X and Y directionscorresponding to the rotation axle and the radius of the tire,respectively, are depicted in FIG. 8. The origin of the reference axismay be chosen so that the X axis is positioned at the bottom of the tiregrooves and the Y axis is positioned on a tire side, as depicted. Stillin an embodiment, coordinates are encoded on two fixed sized numbers,for example two bytes, one for the abscissa X and one for the ordinateY, in such a way that the tire width is equal to the maximum value thatan abscissa X can reach and the tread thickness is equal to the maximumvalue that an ordinate Y can reach. Using such system, the positions ofeach RFID can be expressed as coordinates (i.e., couples of values(X,Y)).

Table 900, depicted on FIG. 9, illustrates an example of the content ofthe special RFID 805 of FIG. 8. Table 900 of FIG. 9 comprises a firstcell 905 wherein the identifier of the tire (‘12345’) can be stored, andas many rows as RFIDs embedded within the tires. Each row, genericallyreferred to as row 910, is divided in three columns. The first column915 is used to store the RFID's identifiers, the second column 920 andthe third column 925 are used to store the RFID's X and Y coordinates,respectively. For example, row 910-i contains the coordinates (127,125)of the RFID having 13 as identifier. It should be noticed that tireidentifier is not required, particularly if an independent reader isassigned to each tire to monitor. Likewise, if the identifiers of theRFIDs correspond to continuous values starting from a predefined value(e.g., 0, 1, 2, . . . ), the values stored in column 915 are notrequired. In an embodiment, the special RFID has a particularidentifier, such as 255 if RFID's identifiers are coded on one byte.This special RFID may also contain other information such as the optimumset width; i.e., the maximum abscissa difference of two RFIDs belongingto a same set.

FIG. 10 shows an example of the algorithm that could be used in order tomonitor a tire having RFIDs embedded according to the fifth embodiment.A first step resets to zero (step 1000) an index i, identifying a set ofRFIDs having approximately equal abscissas X. Then, a first test isperformed to determine whether or not the monitored tire comprises aspecial RFID (SRFID) (step 1005). This test can, for example, determineif the identifier of an RFID corresponds to the identifier assigned tospecial RFIDs. If no special RFID is found, the algorithm uses one ofthe previous described algorithms (FIG. 4 a, 4 b or 7) to monitor thetire. If the tire comprises a special RFID, the content of this specialRFID is read (step 1010) and stored in the reader memory 1015, or in thememory of the processing device, and the number of sets of RFIDs havingapproximately equal abscissas is determined (1020). Then, all the stepsmentioned in box 760 of FIG. 7 (steps 705 to 755) are performed.

A method to determine the number of sets of RFIDs having approximatelyequal abscissas is illustrated on the algorithm depicted of FIG. 11. Thefirst step initializes index j and variable k to zero. Index jcorresponds to the current selected RFID, and variable k is such that(k+1) corresponds to the number of RFID sets, in storing abscissa ofRFID(j), referred to as X(RFID(j)), in variable Xset(k), and indetermining the number Nr of RFIDs embedded within the tire (step 1100).Then index r, identifying the current selected RFID set, is initializedto zero (step 1105). A first test is done to determine whether or notthe distance (distx) between the abscissa of the current selected RFID(RFID(j)) and the abscissa Xset(r) associated to the current selectedset is greater than a predetermined threshold Sw (step 1110). ThresholdSw may be stored in reader memory wherein Sw may have been copied fromthe special RFID. If the distance between the abscissa of the currentselected RFID (RFID(j)) and the abscissa Xset(r) associated to thecurrent selected set is less than threshold Sw, index j is incrementedby one (step 1115), and another test is done to determine whether or notindex j is equal to the number Nr of RFIDs embedded within the tire(step 1120). If index j is not equal to the number Nr, the last foursteps (steps 1105 to 1120) are repeated. If the distance between theabscissa of the current selected RFID (RFID(j)) and the abscissa Xset(r)associated to the current selected set is greater than threshold Sw,index r is incremented by one (step 1125), and another test is done todetermine whether or not index r is equal to the variable k (step 1130).If index r is not equal to the variable k, the last three steps (steps1110 to 1130) are repeated. If index r is equal to the variable k, thevariable k is incremented by one (step 1135), the abscissa of RFID(j),referred to as X(RFID(j)), is stored in variable Xset(k) (step 1140),and the algorithm is branched to step 1115. If index j is equal to thenumber Nr, the variable imax, corresponding to the number of sets ofRFIDs, is set to the value (k+1) (step 1145). The variable imax ispreferably stored in reader memory 1015.

The functions used to determine the tire wear and the tire wear balancemay be adapted to the spatial distribution of the RFIDs. For example,care should be taken if the distribution of the RFIDs along the Y axisis nonlinear (i.e., not spatially uniform), as shown on FIG. 8. In suchcase, considering a set i of RFIDs, the ordinates of which beingexpressed as Y(RFIDs(i)), the following function for determining themeasure of wear TW(i) in Equation (8) can be used:TW(i)=(YNmax(RFID(i))−Ymax(RFID(i)))/YNmax(RFID(i))  (8)

wherein YNmax(RFID(i)) represents the maximum ordinate of the RFIDs ofset i when considering all the RFIDs of this set; i.e., the RFIDs of seti embedded within the tire when it was brand new. Ymax(RFID(i))represents the maximum ordinate of the RFIDs of set i when consideringthe RFIDs of this set at a given time.

In a sixth embodiment, one of the embedded RFIDs, such as the specialRFID, comprises a read-write RFID, the writable memory of this RFIDbeing used to store the history of the tire wear i.e., the time and/ormileage at which each, or some, RFID has(have) been detached from thetire. Such feature allows, in particular, optimization of the tiremanagement of a fleet of vehicles. FIG. 12 illustrates Table 900′,representing a modification of table 900 of FIG. 9 with two additionalcolumns 1200 and 1205 for storing date and mileage, respectively. Forexample, from table 900′, it can be easily determined that RFID havingidentifier 13, positioned at coordinates (127,125), has been lost onDec. 27, 2003, at mileage 12,345. Table 900′ is updated when monitoringthe tire. Each time an event is detected (i.e., the number of RFIDschanges), the system determines which RFIDs have been extracted (i.e.,detached) from a tire, determines a date (called a “detach date”) and/ormileage from the vehicle computer or similar electronic devices storingsuch information, and writes this data in the corresponding cells ofTable 900′ (i.e., in columns 1200 and/or 1205 of the rows correspondingto undetected RFIDs). Naturally, only column 1200 or column 1205 can beused.

In a further embodiment, the writable part of the RFID is used to recordall the events concerning the tire such as pressure variation or changeof wheel position, using the same mechanism as described above. Eachtime a new event is detected, the new event is written in the RFID forfurther processing.

In order to satisfy local and specific requirements, a person skilled inthe art may apply to the solution described above many modifications andalterations, all of which are included within the scope the presentinvention.

1. A method of wear level determination, comprising: distributingmultiple Radio Frequency IDentification (RFID) tags within a thicknessof a wearing surface layer of a tire at an X coordinate and a Ycoordinate, said X coordinate being a coordinate along a rotation axisof the tire, said Y coordinate being a coordinate along a radius of thetire, said wearing surface layer of the tire being an outermost surfacelayer of the tire, said multiple RFID tags and said wearing surfacelayer adapted to be worn away as the tire is being used such that thethickness of the wearing surface layer is reduced as the tire is beingused, said multiple RFID tags consisting of a first plurality of RFIDtags that have not been worn away, a second plurality of RFID tags thathave been worn away, and a special RFID tag that has not been worn away;after said distributing and after the tire has been mounted on a vehicleand after the second plurality of tags has been worn away and while thefirst plurality of tags has not been worn away and while the specialRFID tag has not been worn away, receiving data from the first pluralityof RFID tags and from a table in the special RFID tag; and determining ameasure of wear of the wearing surface layer of the tire from saidreceived data, wherein the table in the special RFID tag comprises: anidentifier of each RFID tag of the first plurality of RFID tags, the Xcoordinate and the Y coordinate of each RFID tag of the first pluralityof RFID tags, an identifier of each RFID tag of the second plurality ofRFID tags, and the X coordinate and the Y coordinate at which each RFIDtag of the second plurality of RFID tags had been disposed in thewearing surface layer before being worn away.
 2. The method of claim 1,wherein the table in the special RFID tag further comprises anidentifier of the tire.
 3. The method of claim 1, wherein the table inthe special RFID tag further comprises a date and milage of the vehicleat which each RFID tag of the second plurality of RFID tags had beenworn away.
 4. The method of claim 1, wherein the table in the specialRFID tag comprises a first plurality of rows and a second plurality ofrows; wherein each row of the first plurality of rows corresponds to aRFID tag of the first plurality of RFID tags and comprises an identifierof its corresponding RFID tag and both the X coordinate and the Ycoordinate of its corresponding RFID tag; and wherein each row of thesecond plurality of rows is associated with a RFID tag of the secondplurality of RFID tags and comprises an identifier of its associatedRFID tag, the X coordinate and the Y coordinate at which its associatedRFID tag had been disposed in the wearing surface layer before beingworn away.
 5. The method of claim 1, wherein said determining themeasure of wear comprises: classifying, from the received data, theRFIDs of the first and second plurality of RFID tags into N sets ofRFIDs such that N is at least 2; and for set i of the N sets (i=1, 2, .. . , N), computing a measure of wear TW(i).
 6. The method of claim 5,wherein each set of the N sets is characterized by the X coordinate ofall RFIDs in each set not deviating from each other by more than apredetermined threshold Sw, and wherein the special RFID tag stores anoptimum maximum deviation among the X coordinates of all RFIDs in anysame set of the N sets.
 7. The method of claim 6, wherein said computingTW(i) comprises computing TW(i) viaTW(i)=(YNmax(RFID(i))−Ymax(RFID(i)))/YNmax(RFID(i)), whereinYNmax(RFID(i)) is a maximum Y coordinate of all RFIDs in set i, andwherein Ymax(RFID(i)) is a maximum Y coordinate of the RFIDs in set ithat are comprised by the first plurality of RFID tags.
 8. A product,comprising: a wearing surface layer of a tire; multiple Radio FrequencyIDentification (RFID) tags within a thickness of the wearing surfacelayer at an X coordinate and a Y coordinate, said X coordinate being acoordinate along a rotation axis of the tire, said Y coordinate being acoordinate along a radius of the tire, said wearing surface layer of thetire being an outermost surface layer of the tire, said multiple RFIDtags and said wearing surface layer adapted to be worn away as the tireis being used such that the thickness of the wearing surface layer isreduced as the tire is being used, said multiple RFID tags consisting ofa first plurality of RFID tags that have not been worn away and aspecial RFID tag that has not been worn away; and means for determininga measure of wear of the wearing surface layer of the tire from datareceived from the first plurality of RFID tags and from a table in thespecial RFID tag, wherein the table in the special RFID tag comprises:an identifier of each RFID tag of the first plurality of RFID tags, theX coordinate and the Y coordinate of each RFID tag of the firstplurality of RFID tags, an identifier of each RFID tag of a secondplurality of RFID tags that had previously been disposed in the wearingsurface layer and have been worn away, and the X coordinate and the Ycoordinate at which each RFID tag of the second plurality of RFID tagshad been disposed in the wearing surface layer before being worn away.9. The product of claim 8, wherein the table in the special RFID tagfurther comprises an identifier of the tire.
 10. The product of claim 8,wherein the table in the special RFID tag further comprises a date andmilage of the vehicle at which each RFID tag of the second plurality ofRFID tags had been worn away.
 11. The product of claim 8, wherein thetable in the special RFID tag comprises a first plurality of rows and asecond plurality of rows; wherein each row of the first plurality ofrows corresponds to a RFID tag of the first plurality of RFID tags andcomprises an identifier of its corresponding RFID tag and both the Xcoordinate and the Y coordinate of its corresponding RFID tag; whereineach row of the second plurality of rows is associated with a RFID tagof the second plurality of RFID tags and comprises an identifier of itsassociated RFID tag, the X coordinate and the Y coordinate at which itsassociated RFID tag had been disposed in the wearing surface layerbefore being worn away.
 12. The product of claim 8, wherein said meansfor determining the measure of wear comprises: means for classifying,from the received data, the RFIDs of the first and second plurality ofRFID tags into N sets of RFIDs such that N is at least 2; and for set iof the N sets (i=1, 2, . . . , N), means for computing a measure of wearTW(i).
 13. The product of claim 12, wherein each set of the N sets ischaracterized by the X coordinate of all RFIDs in each set not deviatingfrom each other by more than a predetermined threshold Sw, and whereinthe special RFID tag stores an optimum maximum deviation among the Xcoordinates of all RFIDs in any same set of the N sets.
 14. The productof claim 13, wherein said means for computing TW(i) comprises means forcomputing TW(i) as a function of YNmax(RFID(i)) and Ymax(RFID(i)),wherein YNmax(RFID(i)) is a maximum Y coordinate of all RFIDs in set i,and wherein Ymax(RFID(i)) is a maximum Y coordinate of the RFIDs in seti that are comprised by the first plurality of RFID tags.